Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$139.97	6.367%	$148.8819	$148.88	$148.90	$148.90
Purchase #2	$247.87	8.734%	$269.519	$269.52	$269.50	$269.50
Purchase #3	$212.43	8.555%	$230.6034	$230.60	$230.60	$230.60
Purchase #4	$240.29	13.133%	$271.8473	$271.85	$271.85	$271.80
Purchase #5	$63.33	6.251%	$67.2888	$67.29	$67.30	$67.30
Purchase #6	$89.30	11.360%	$99.4445	$99.44	$99.45	$99.40
Purchase #7	$79.65	3.858%	$82.7229	$82.72	$82.70	$82.70
7 purchase totals =	$1,072.84		$1,170.3078	$1,170.30	$1,170.30	$1,170.20